[Insight-users] Very Basic ITK Question

[Luis Ibanez]

Hi Rashdek,


1) You should have posted in your email the typedefs that you
    used for declaring the GaussianDerivativeImageFunction
    type...


    If you want to have consistent types, you must use the
    traits of the classes.

    In your particular case, instead of declaring the PointType
    on your own, you should use the PointType trait, like in the
    following code:


    typedef itk::Image< char, 3 >    ImageType;

    typedef itk::GaussianDerivativeImageFunction<
      ImageType, double > GaussianDerivativeFunctiontType;


    GaussianDerivativeFunctiontType::Pointer function =
       GaussianDerivativeFunctiontType::New();

    function->SetImage( reader->GetOutput() );

    function->SetSigma( 1.8 );

    typedef GaussianDerivativeFunctiontType::PointType  PointType;

    PointType point;

    point[0] = 10.9;
    point[1] = 20.7;
    point[2] = 30.2;

    typedef GaussianDerivativeFunctiontType::VectorType  VectorType;

    VectorType gradient = function->Evaluate( point );


    Since the types PointType and VectorType were taken
    directly from the GradientDerivativeFunction type
    this ensures that all types will be consistent.




2) In order to compute the Hessian of an image you need the
    Second derivatives.  The GaussianDerivativeImageFunction
    class will only compute the first derivatives.  You may
    have to modify the code of this class...




    Regards,


       Luis



-------------
rashedk wrote:
> Hi everyone, 
> 
> I am trying to Evaluate the Hessian at a 3D point. I am looking at these
> functions of GaussianDerivativeImageFunction
> 
> virtual OutputType 	Evaluate (const InputType &input) const=0
> virtual TOutput 	Evaluate (const PointType &point) const=0
> virtual OutputType 	Evaluate (const PointType &point) const
> 
> How do I use Evaluate?? I tried creating a 3D point using: 
> typedef itk::Point< int, Dimension > PointType;
> PointType point;
> point[0] = 5; // x coordinate
> point[1] = 5; // y coordinate
> point[2] = 5; // z coordinate
> 
> But when i feed this into Evaluate, it doesnt compile. It expects a
> PointType& and i can't seem to be able to convert PointType to PointType& 
> 
> Thanks, 
> Rashed 
> 
>